This project is designed to determine the mechanism responsible for increased orotic acid excretion in animals consuming diets that are marginal or deficient in arginine or other urea cycle intermediates. The present studies will determine the involvement of the urea cycle and the shunting of excess nitrogen in pyrimidine biosynthesis. Studies will examine the influence of arginine deficiency and amino acid excess on the shunting of nitrogen from urea biosynthesis into pyrimidine biosynthesis. Additionally, the capacity of the urea cycle to detoxify ammonia as indicated by the flux of nitrogen through the pathway and enzymatic activities will be determined. These studies will also examine some of the long term complications of consumption of a diet that is deficient in arginine or other urea cycle intermediates in the rat.